The overall objective of this proposal is to study human visual functioning, both retinal and cortical, by means of the ERG and the cortical evoked response. Both basic experimental and clinical research studies are proposed. One project is to determine the sites of origin of the visual evoked response resulting from the stimulation of local retinal areas. From potential contour mapping and consideration of theoretical dipole sources, it is proposed to determine whether the early components of the visual evoked response originate in geniculo-calcarine radiations or primary visual cortex. Other basic parameters controlling the visual evoked response, such as stimulus area, will be investigated. From the results on normal subjects, it is expected that better clinical procedures can be derived that will be tested on patients with hemianopia and optic nerve disease. It is also proposed to evaluate a pattern ERG test on patients with retinal disease to determine its utility.